High error rate on one downstream channel

For some time now I have been getting a very high error rate on one downstream channel on my Arris SB8200 V6. This is accompanied by repeated errors in the error log as shown below. (I have obscured the CM-MAC address).

Is this a problem with Comcast equipment, or interference from some local 591 MHz radiation source? I don't know of anything in our house that would source that frequency.

						Corrected	Uncorrected
26	Locked	QAM256	585000000 Hz	-4.5 dBmV	37.5 dB	7899	0
27	Locked	QAM256	591000000 Hz	-4.4 dBmV	26.7 dB	103382321	182118309
28	Locked	QAM256	597000000 Hz	-4.5 dBmV	37.6 dB	7437	0

02/05/2024 13:03	74010100	6	"CM-STATUS message sent. Event Type Code: 4; Chan ID: 27; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;"
02/05/2024 13:02	84020300	5	"MDD message timeout;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;"

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Accepted Solution

trsm3

Frequent Visitor

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24 Messages

1 year ago

Just to close this out, this happened at the time speeds were being increased. The frequencies showing interference closely matched some strong local broadcast TV frequencies, but that could be coincidence. I ended up making no changes myself other than rebooting the modem a few times to see where things stood. The signal eventually quieted down around the beginning of April following a few automatic restarts.

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EG

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110.4K Messages

Hope things hold up for you good luck ! Please feel free to create a new topic if the problem returns. Closing this marked as "Solved" thread.

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1 year ago

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XfinityAirelle

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2.6K Messages

1 year ago

trsmith3

Hi there! Our awesome digital care team would be happy to assist you. Can you initiate a direct message and start with your full name and address? To start a direct message, you must be signed in. Please click the "Direct Messaging" icon in the top right of the page next to the bell, and send your message to "Xfinity Support". Talk to you there!

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trsm3

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24 Messages

Thanks, but there is no "To" field in the direct message and there has been no reply to the message I did send.

Since you have all the information you need to contact me, I would suggest that if Comcast has an actual interest in following up, they initiate an actual followup.

Regards.

1 year ago

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XfinityAldrik

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2.2K Messages

Thank you for letting us known @trsmith3! Here's the detailed steps to direct message us:

• Click "Sign In" if necessary
• Click the "Direct Messaging" icon or https://forums.xfinity.com/direct-messaging

• Click the "New message" (pencil and paper) icon
From here there should be a "to" field.

The "To:" line should prompt you to "Type the name of a person". Instead, type "Xfinity Support" there

• As you are typing a drop-down list appears. Select "Xfinity Support" from that list

• An "Xfinity Support" graphic replaces the "To:" line

Type your message in the text area near the bottom of the window

Press Enter to send it.

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Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
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1 year ago

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trsm3

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24 Messages

1 year ago

Thank you. I will try again.

For the record, the problem went away shortly before the first reply here. Since then it has gotten worse with excessive errors on 5 channels and a constant stream of errors in the log.

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trsm3

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24 Messages

I did manage to send a message to support, but no response. However, the number of noisy channels has increased, power levels are lower on all channels, and SNR levels are higher on the problem channel(s).

Ch		Modulation	Frequency	Power	SNR	Corrected	Uncorrectable
26	Locked	QAM256	585000000 Hz	-6.8 dBmV	37.5 dB	7770	41
27	Locked	QAM256	591000000 Hz	-7.0 dBmV	37.9 dB	96753363	204033766
28	Locked	QAM256	597000000 Hz	-7.0 dBmV	37.6 dB	7144	193
...
32	Locked	QAM256	621000000 Hz	-7.6 dBmV	37.6 dB	8491	401
33	Locked	QAM256	627000000 Hz	-7.9 dBmV	37.2 dB	95060742	26704102
34	Locked	QAM256	633000000 Hz	-7.9 dBmV	32.5 dB	171309353	63179763
35	Locked	QAM256	639000000 Hz	-7.9 dBmV	35.6 dB	201308	1331
...
41	Locked	QAM256	675000000 Hz	-9.3 dBmV	37.2 dB	7752	365
42	Locked	QAM256	681000000 Hz	-8.9 dBmV	37.6 dB	1540785	2717601
43	Locked	QAM256	687000000 Hz	-8.6 dBmV	37.5 dB	2744533	10321986
44	Locked	QAM256	693000000 Hz	-8.4 dBmV	37.5 dB	5911	848

1 year ago

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EG

Expert

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110.4K Messages

@trsmith3

Have you tried to see if any of those troubleshooting tips in the link to the article that @BruceW you apply ?

(edited)

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1 year ago

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trsm3

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24 Messages

I went through all those that are relevant before I posted here to begin with.

1 year ago

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EG

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110.4K Messages

@trsmith3

OK, well that wasn't apparent.. Good luck !

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1 year ago

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BruceW

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26.4K Messages

1 year ago

... 591000000 Hz -4.4 dBmV 26.7 dB ...

The SNR on this channel is out of spec (too low). If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you still need help you'll have to have one of their techs out to identify the cause and correct it.

If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit (approx $100) unless you have their Service Protection Plan ( https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device or anything outside your home you shouldn't be charged.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

(edited)

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trsm3

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Yes, an SNR that is too low would certainly be consistent with a high noise level.

When it's only on a single channel, it seems unlikely to be because of a cable or connector. That would be evident across the board. Far more likely to be a faulty amplifier at the head end or a strong external signal at that frequency somewhere along the transmission path.

The misbehaving channels now all have SNRs of 36.4 to 38 and signal strengths of -7.7 to -9.7 dBmV, so something has changed.

1 year ago

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BruceW

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26.4K Messages

1 year ago

... When it's only on a single channel, it seems unlikely to be because of a cable or connector. That would be evident across the board. ...

RF signals often behave in ways that are contrary to intuition. Although I can't say whether the problem you are having is a nearby cable/connector problem or something farther upstream, cable/connector problems can indeed cause trouble for just a single channel, a group of channels, or for all of them. You need someone with appropriate training and equipment to determine the cause.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

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EG

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110.4K Messages

1 year ago

Yep. @BruceW is correct. Standing waves / micro reflections / spurious noise ingress due to a hardware impairment somewhere can indeed affect a single channel.

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Your Home Network

trsm3

High error rate on one downstream channel

trsm3

EG

XfinityAirelle

trsm3

XfinityAldrik

trsm3

trsm3

EG

trsm3

EG

BruceW

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

trsm3

BruceW

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

EG

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